feat(freertos): added POSIX/Linux simulator port to FreeRTOS SMP

* Added a POSIX/Linux simulator that is compatible with the Amazon
  FreeRTOS SMP API. Note that the simulator itself is still
  single core, like the IDF FreeRTOS POSIX/Linux simulator.

components/freertos/FreeRTOS-Kernel-SMP/portable/linux/include/spinlock.h

@@ -0,0 +1,59 @@
+/*
+ * SPDX-FileCopyrightText: 2015-2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * This file provides only very simple stubs to build IDF-based FreeRTOSes which use spinlocks on Linux.
+ */
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define SPINLOCK_FREE          0xB33FFFFF
+#define SPINLOCK_WAIT_FOREVER  (-1)
+#define SPINLOCK_NO_WAIT        0
+#define SPINLOCK_INITIALIZER   {.owner = SPINLOCK_FREE,.count = 0}
+#define CORE_ID_REGVAL_XOR_SWAP (0xCDCD ^ 0xABAB)
+
+/**
+ * @brief Spinlock object
+ * Owner:
+ *  - Set to 0 if uninitialized
+ *  - Set to portMUX_FREE_VAL when free
+ *  - Set to CORE_ID_REGVAL_PRO or CORE_ID_REGVAL_AP when locked
+ *  - Any other value indicates corruption
+ * Count:
+ *  - 0 if unlocked
+ *  - Recursive count if locked
+ *
+ * @note The simulator is single-core, hence, it doesn't have a proper spinlock implementation.
+ * @note Keep portMUX_INITIALIZER_UNLOCKED in sync with this struct
+ */
+typedef struct {
+    uint32_t owner;
+    uint32_t count;
+}spinlock_t;
+
+static inline void __attribute__((always_inline)) spinlock_initialize(spinlock_t *lock)
+{
+}
+
+static inline bool __attribute__((always_inline)) spinlock_acquire(spinlock_t *lock, int32_t timeout)
+{
+    return true;
+}
+
+static inline void __attribute__((always_inline)) spinlock_release(spinlock_t *lock)
+{
+}
+
+#ifdef __cplusplus
+}
+#endif